Insulators have been made with various materials. For example, insulators have been made of a ceramic or porcelain material. The ceramic and porcelain insulators, however, are heavy and bulky; they require specialized assembly fixtures or processes and are awkward and difficult to handle and ship. The ceramic insulators are brittle and easily chipped or broken.
As noted in Application Ser. No. 10/173,386, filed on Jun. 16, 2002, entitled “Composite Insulator for Fuse Cutout,” the disclosure of which is incorporated herein by reference, problems have arisen with electrical insulators. One such problem occurs when electricity flashes directly from a conducting surface to a grounded surface. This phenomenon is referred to as “flashover.” The electricity travel gap between the conducting surface and the grounded surface is called the “strike distance.”
Another problem occurs when the electrical current travels or “creeps” along the surface of the insulator. “Creep” results when the insulator has an inadequate surface distance. This may occur when water, dirt, debris, salts, air-borne material, and air pollution is trapped at the insulator surface and provide an easier path for the electrical current. This surface distance may also be referred to as the “leakage,” “tracking,” or “creep” distance.
Because of these problems, insulators must be made of many different sizes so as to provide different strike and creep distances, as determined by operating voltages and environmental conditions. The strike distance in air is known, thus insulators must be made of various sizes in order to increase this distance and match the appropriate size insulator to a particular voltage. Creep distance must also be increased as voltage across the conductor increases so that flashover can be prevented.
Plastic or polymeric insulators have been designed to overcome some of the problems with conventional insulators. However, none of the prior plastic insulators have solved some or all of the problems simultaneously. For example, polymeric insulators have been made with “fins” or “sheds” which require time and labor for assembly. U.S. Pat. No. 4,833,278 to Lambeth, entitled “Insulator Housing Made From Polymeric Materials and Having Spirally Arranged Inner Sheds and Water Sheds,” the disclosure of which is hereby incorporated herein by reference, discloses a resin bonded fiber tube made through filament winding (Col 5, ll. 15-17) with spiral ribs of fiberglass and resin to support a series of circular “sheds” (Col. 5, ll. 28-31; see also FIG. 1).
Other insulators require a complicated assembly of metal end fittings. For example, an electrical insulator is disclosed in U.S. Pat. No. 4,440,975 to Kaczerginski, entitled “Electrical Insulator Including a Molded One-Piece Cover Having Plate-like Fins with Arcuately Displaced Mold Line Segments,” the disclosure of which is incorporated herein by reference. However, the insulator of Kaczerginski involves a more complicated assembly of two end pieces and an insulating rod of an undisclosed material. Col. 1, ll. 66-68. Similarly, in U.S. Pat. No. 4,246,696 to Bauer et al., the disclosure of which is incorporated herein by reference, an insulator having a prefabricated glass fiber rod manufactured through a pultrusion process is disclosed. Col. 3, ll. 47-49. Yet, the insulator of Bauer et al. requires a complicated attachment of metallic suspension fittings by fanning out the fiber reinforced stalk or by forcing the fittings on by pressure. Col. 3, line 67 to Col. 4, line 2.
Therefore, there exists a need for simple design that facilitates ease in the manufacture of the many different-sized cutouts and insulators the electrical power industry requires. There also exists a need for a lighter insulator that allows for greater ease in handling and shipping. Further, there exists a need for an insulator, which will not trap water, dirt, debris, salts, and air-borne material and thereby reduce the effective creep distance. Finally, there exists a need for a stronger insulator, which will not chip or break during shipping and handling.
The present invention is directed to overcoming these and other disadvantages inherent in prior-art systems.